Thin film transistor and method for producing the same

ABSTRACT

The present invention provides a method of manufacturing a thin film transistor of a top-contact structure with suppressed deterioration by a process which is easy and suitable for increase in area without damaging an organic semiconductor pattern. The organic semiconductor pattern is formed on a substrate. An electrode material film is formed on the substrate so as to cover the organic semiconductor pattern. A resist pattern is formed on the electrode material film. By wet etching using the resist pattern as a mask, the electrode material film is patterned. By the process, a source electrode and a drain electrode are formed.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/448,969 filed on Apr. 17, 2012, which is a continuation ofU.S. patent application Ser. No. 13/176,443 filed on Jul. 5, 2011,issued on Aug. 28, 2012 as U.S. Pat. No. 8,253,133, which is adivisional of U.S. patent application Ser. No. 12/627,434 filed on Nov.30, 2009, issued on Aug. 30, 2011 as U.S. Pat. No. 8,008,115, whichclaims priority to Japanese Patent Application JP 2008-303432 filed inthe Japanese Patent Office on Nov. 28, 2008, the entire contents ofwhich is being incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to a method of manufacturing a thin filmtransistor, a thin film transistor, and an electronic device. Moreparticularly, the invention relates to a method of manufacturing a thinfilm transistor in which fine source and drain electrodes are formedover an organic semiconductor pattern, a thin film transistor obtainedby the method, and an electronic device using the thin film transistor.

2. Description of the Related Art

In recent years, attention is paid to a thin film transistor (TFT) usingan organic semiconductor as a channel layer, a so-called organic TFT.Since the organic TFT is formed by applying a channel layer made oforganic semiconductor at low temperature, it is advantageous toreduction of cost. The organic TFT is also formed on a flexiblesubstrate having no heat resistance property such as a plasticsubstrate. It is known that, in an organic TFT having a top-contactbottom-gate structure, deterioration in characteristics due to stress ofheat or the like is suppressed as compared with an organic TFT having abottom-contact structure.

In manufacture of such an organic TFT of the top-contact bottom-gatestructure, a method of patterning a source electrode and a drainelectrode with high precision on an organic semiconductor pattern isbeing examined. For example, Japanese Unexamined Patent ApplicationPublication No. 2006-216718 discloses a method of providing anintersecting part which halves a space above a substrate, forming anorganic semiconductor pattern by vapor deposition from two directions,and vapor-depositing a metal material so as to be divided by theintersecting part, thereby forming a source electrode and a drainelectrode.

SUMMARY

However, in the manufacturing method using the intersecting part whichhalves a space above a substrate, formation of the intersection part istroublesome, and it is difficult to form a source electrode and a drainelectrode with unifoim precision over a substrate of large area.

It is therefore desirable to provide a method of manufacturing a thinfilm transistor of a top-contact structure with suppressed deteriorationby a process which is easy and suitable for increase in area withoutdamaging an organic semiconductor pattern, a thin film transistor havinga top-contact structure obtained by applying the method and, further, anelectronic device having the thin film transistor.

A method of manufacturing a thin film transistor of the presentinvention for achieving such a purpose is performed by the followingprocedure.

First, an organic semiconductor pattern is formed on a substrate. Next,an electrode material film is formed on the substrate so as to cover theorganic semiconductor pattern. After that, a resist pattern is formed onthe electrode material film, and a source electrode and a drainelectrode obtained by patterning the electrode material film by wetetching using the resist pattern as a mask are formed.

In the method of manufacturing a thin film transistor, the electrodematerial film is etched using the resist pattern as a mask, so that thesource electrode and the drain electrode patterned with high precisionare formed. Since wet etching is performed as the etching of theelectrode material film, the organic semiconductor layer under theelectrode material film is prevented from being damaged. Further, sincethe etching process using the resist pattern as a mask is performed, themethod is easy and suitable for increase in area.

A thin film transistor as an embodiment of the present invention isformed by the above-described method and has: an organic semiconductorpattern provided on a substrate; and a source electrode and a drainelectrode provided over the substrate in a state where they are isolatedfrom each other above the semiconductor pattern. In particular, each ofthe source and drain electrodes has an end face shape which isisotropically etched.

According to a method of manufacturing a thin film transistor of anembodiment of the invention, while applying a process which is easy andsuitable for increase in area, a thin film transistor of a top-contactstructure with suppressed deterioration is obtained with high precisionwithout damaging an organic semiconductor pattern. By using a thin filmtransistor obtained in such a manner, an electrode device withsuppressed deterioration is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1D are sectional process drawings (No. 1) for explaining afirst embodiment of the present invention.

FIGS. 2A to 2D are sectional process drawings (No. 2) for explaining thefirst embodiment.

FIG. 3 is a schematic plan view of a thin film transistor of a topcontact structure to which the present invention is applied.

FIGS. 4A and 4B are sectional process drawings for explaining acharacteristic part of a second embodiment.

FIGS. 5A to 5D are sectional process drawings for explaining acharacteristic part of a third embodiment.

FIGS. 6A to 6D are sectional process drawings (No. 1) for explaining afourth embodiment.

FIGS. 7A to 7C are sectional process drawings (No. 2) for explaining thefourth embodiment.

FIGS. 8A to 8D are sectional process drawings (No. 1) for explaining afifth embodiment.

FIGS. 9A to 9C are sectional process drawings (No. 2) for explaining thefifth embodiment.

FIGS. 10A to 10D are sectional process drawings for explaining a sixthembodiment.

FIG. 11 is a characteristic diagram for explaining an effect of thesixth embodiment.

FIGS. 12A to 12D are sectional process drawings for explaining a seventhembodiment.

FIGS. 13A to 13C are sectional process drawings for explaining an eighthembodiment.

FIG. 14 is a circuit diagram expressing an example of application to adisplay device.

FIG. 15 is a cross section of one pixel in the display device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described with reference tothe drawings below in the following order.

1. First embodiment (method of manufacturing a thin film transistor)

2. Second embodiment (an example of over-etching an organicsemiconductor pattern)

3. Third embodiment (an example of leaving a protection film pattern onan organic semiconductor pattern)

4. Fourth embodiment (an example of using a carrier injection materialas a protection film and a protection film pattern and leaving them)

5. Fifth embodiment (an example of using a protection film pattern as astacking structure and leaving it)

6. Sixth embodiment (an example of reducing contact resistance)

7. Seventh embodiment (another example of reducing contact resistance)

8. Eight embodiment (another example of reducing contact resistance)

9. Example of application to electronic device (display device)

1. First embodiment

FIGS. 1A to 1D and FIGS. 2A to 2D are sectional process drawings of afirst example of applying a method of manufacturing a thin filmtransistor according to a first embodiment of the present invention tomanufacture of a top-contact bottom-gate structure. FIG. 3 is a planview of a thin film transistor of the top-contact bottom-gate structuremanufactured in the example. In the following, according to thesectional process drawings of FIGS. 1A to 1D and FIGS. 2A to 2D,referring to FIG. 3, the manufacturing method of the first embodimentwill be described.

First, as illustrated in FIG. 1A, a gate electrode 3 is formed in apattern on an insulating substrate 1, a gate insulating film 5 is formedso as to cover the gate electrode 3 and, further, an organicsemiconductor layer 7 is formed on the gate insulating film 5. Theprocesses are performed in a normal procedure, for example, as follows.

The gate electrode 3 is formed in a pattern, for example, by forming ametal material film of gold (Au), platinum (Pt), silver (Ag), tungsten(W), tantalum (Ta), molybdenum (Mo), aluminum (Al), chromium (Cr),titanium (Ti), copper (Cu), nickel (Ni), or the like. The metal materialfilm is formed by, for example, sputtering, vapor deposition, plating,or the like. After that, a resist pattern (not shown) is formed on themetal material film by photolithography. Using the resist pattern as amask, the metal material film is etched to obtain the gate electrode 3.The method of forming the gate electrode 3 is not limited to theabove-described method but printing or the like may be applied.

When the gate insulating film 5 is made of an inorganic material such assilicon oxide or silicon nitride, the gate insulating film 5 is formedby CVD or sputtering. On the other hand, when the gate insulating film 5is made of an organic highpolymer material such as polyvinylphenol,PMMA, polyimide, fluorine resin, or the like, the gate insulating film 5is formed by coating or printing.

The organic semiconductor layer 7 is formed by applying a film formingmethod which is properly selected according to a material used.

Examples of the organic semiconductor material to be used are asfollows.

polypyrrole and polypyrrole substitute,

polythiophene and polythiophene substitute,

isothianaphthenes such as polyisothianaphthene,

chenylene vinylenes such as polychenylene vinylene,

poly(p-phenylenevinylenes) such as poly(p-phenylenevinylene),

polyaniline and polyaniline substitute,

polyacetylenes,

polydiacetylenes,

polyazulenes,

polypyrenes,

polycarbazoles,

polyselenophenes,

polyfurans,

poly(p-phenylenes),

polyindoles,

polypyridazines,

polymers and polycyclic condensate such as polyvinyl carbazole,polyphenylene sulfide, or polyvinylene sulfide,

derivatives (triphenodioxazine, triphenodithiazine, hexacene-6,15-quinone, or the like) obtained by substituting oligomers having thesame repeating unit as that of the polymer in the material, acenes suchas naphthacene, pentacene, hexacene, dibenzopentacene,tetrabenzopentacene, pyrene, dizenzopyrene, chrysene, perylene,coronene, terrylene, ovalene, quaterrylene, and circumanthracene, and apart of carbon in the acenes with a functional group such as atoms of N,S, O, or the like, a carbonyl group, or the like,

metal phthalocyanines,

tetrathiafulvalene and tetrathiafulvalene derivatives,

tetrathiapentalene and tetrathiapentalene derivatives,

naphthalene 1,4,5,8-tetracarboxylic acid diimide,N,N′-bis(4-trifuoromethyl benzyl)naphthalene 1,4,5,8-tetracarboxylicacid diimide, N,N′-bis(1H, 1H-perfluorooctyl), N,N′-bis(1H,1H-perfluorooctyl), and N,N′-dioctylnaphthalene 1,4,5,8-tetracarboxylicacid diimide derivative,

naphthalene tetracarboxylic acid diimides such as naphthalene 2,3,6,7tetracarboxylic acid diimide,

condensed-ring tetracarboxylic acid diimides such as anthracenetetracarboxylic acid diimides like anthracene 2,3,6,7-tetracarboxylicacid diimide,

fullerenes such as C60, C70, C76, C78, and C84,

carbon nanotube such as SWNT, and

pigments such as merocyanine dyes and hemicyanine dyes.

The organic semiconductor layer 7 made of any of the above materials maybe formed by applying a method properly selected from the vacuumdeposition methods such as resistance heating evaporation and sputteringand the coating method such as spin coating in accordance with amaterial to be used. Examples of the coating method include air doctorcoating, blade coating, rod coating, knife coating, squeeze coating,reverse roll coating, transfer roll coating, gravure coating, kisscoating, cast coating, spray coating, slit orifice coating, calendarcoating, and dip coating.

For example, as the organic semiconductor layer 7, a film made ofpentacene and having a thickness of 50 nm is formed by vacuumevaporation.

As shown in FIG. 1B, a protection film 9 is formed on the organicsemiconductor layer 7. The protection film 9 is made of, for example, ametal material. Examples of the metal material of the protection film 9include gold (Au), platinum (Pt), palladium (Pd), silver (Ag), tungsten(W), tantalum (Ta), molybdenum (Mo), aluminum (Al), chromium (Cr),titanium (Ti), copper (Cu), nickel (Ni), indium (In), tin (Sn),manganese (Mn), ruthenium (Rh), rubidium (Rb), and their compounds. Theprotection film 9 may have a stacked structure of the above-describedmaterials.

The protection film 9 may be formed by applying a method properlyselected from the resistance heating evaporation, the vacuum depositionmethod such as sputtering, or the above-described various coatingmethods.

For example, a film made of gold (Au) is formed by vacuum deposition asthe protection film 9.

By forming the protection film 9 made of the metal material in contactwith the organic semiconductor layer 7, a metal material component A ofthe protection film 9 is slightly diffused into the surface layer of theorganic semiconductor layer 7.

Next, as shown in FIG. 1C, a resist pattern 11 is formed on theprotection film 9 in a position above the gate electrode 3. The resistpattern 11 is formed by applying the lithography method or the printingmethod. As the printing method, ink jet printing, screen printing,offset printing, gravure printing, flexographic printing, micro-contactprinting, or the like may be used. In formation of the resist pattern11, the organic semiconductor layer 7 is protected by the protectionfilm 9

Subsequently, using the resist pattern 11 as a mask, the protection film9 is etched to form a protection film pattern 9 a on the organicsemiconductor layer 7. As the etching for the protection film 9, wetetching is employed.

As etchant, for example, a solution made of acid such as nitric acid,sulfuric acid, hydrochloric acid, acetic acid, oxalic acid, hydrofluoricacid, or hydrogen peroxide, salt such as ammonium fluoride, potassiumiodide, peimanganate, or bichromate, or mixture of the acid and the saltis used. To suppress damage on the organic semiconductor layer 7, theconcentration of acids in the etchant is preferably 20% or less. Toassure stable etching rate, an additive such as an organic nitrogencompound may be added.

After the protection film pattern 9 a is formed by wet etching, theresist pattern 11 is removed. The resist pattern 11 is removed bydissolution cleaning removal by a wet process or aching (dry etching).At the time of removing the resist pattern 11, the organic semiconductorlayer 7 is protected by the protection film 9

Next, as illustrated in FIG. 1D, using the protection film pattern 9 aas a mask, the organic semiconductor layer 7 is etched and, in a statewhere a part on the gate electrode 3 is covered in the width directionof the gate electrode 3, an organic semiconductor pattern 7 a is formedby dry etching. By the process, the thin film transistor to be formed isisolated.

As illustrated in FIG. 2A, the protection film pattern 9 a is peeledoff. The peel-off of the protection film pattern 9 a is performed by wetetching. An etchant similar to that used at the time of forming theprotection film pattern 9 a by etching the protection film 9 is used.

As illustrated in FIG. 2B, in a state where the organic semiconductorpattern 7 a is covered, an electrode material film 13 is formed on thegate insulating film 5. The electrode material film 13 is provided toform a source electrode and a drain electrode and is made of a material,in a metal material or an organic conductive material, by which the filmis formed without damaging the organic semiconductor pattern 7 a and isin ohmic-contact with the organic semiconductor pattern 7 a. The samematerial as that of the protection film 9 is used, and the electrodematerial film 13 is formed similarly. Particularly, from the viewpointof ohmic-contact with the organic semiconductor pattern 7 a, gold (Au),platinum (Pt), silver (Ag), copper (Cu), aluminum (Al), nickel (Ni),chromium (Cr), molybdenum (Mo), alloys and oxides of those elements, andthe like are preferably used.

In this case, for example, a film made of gold (Au) is formed as theelectrode material film 13 by the vacuum deposition method.

Next, as shown in FIG. 2C, a resist pattern 15 is formed on theelectrode material film 13. The resist pattern 15 is formed by applyingthe lithography or printing method. As the printing method, ink jetprinting, screen printing, offset printing, gravure printing,flexographic printing, micro-contact printing, or the like may be used.In formation of the resist pattern 15, the organic semiconductor pattern7 a is protected by the electrode material film 13.

Subsequently, using the resist pattern 15 as a mask, the electrodematerial film 13 is etched. By the operation, a source electrode 13 sand a drain electrode 13 d are formed, which are isolated from eachother above the organic semiconductor pattern 7 a and have a shape thatan end portion is stacked on the organic semiconductor pattern 7 a inpositions where they face each other while sandwiching the gateelectrode 3.

As the etching for the electrode material film 13, wet etching isemployed. As etchant, an etchant similar to that for the protection film9 is used. By an effect of the metal material component A of theprotection film 9 slightly diffused into the surface layer of theorganic semiconductor pattern 7 a, corrosion caused by the etchant forthe organic semiconductor pattern 7 a is prevented. By the wet etching,an etchant component B in the etchant is slightly diffused in thesurface layer of the semiconductor pattern 7 a.

After the source electrode 13 s and the drain electrode 13 d are formedby wet etching, the resist pattern 15 is removed. Removal of the resistpattern 15 is performed in a manner similar to that of the resistpattern 11.

As a result, a thin film transistor 20-1 having the top-contactbottom-gate structure shown in FIGS. 2D and 3 is obtained.

In the thin film transistor 20-1 obtained in such a manner, an end faceof each of the source electrode 13 s and the drain electrode 13 disolated from each other above the organic semiconductor pattern 7 a hasa shape which is isotropically etched by wet etching.

In the first embodiment, the source electrode 13 s and the drainelectrode 13 d are shaped by etching the electrode material film 13using the resist pattern 15 as a mask. Consequently, the sourceelectrode 13 s and the drain electrode 7 s patterned with high precisionmay be formed. The etching for the electrode material film 13 is wetetching, thereby preventing the organic semiconductor pattern 7 a as anunder layer from being damaged. Since the process is an etching processusing the resist pattern as a mask, it is easy and is also suitable toincrease the area.

As a result, while applying the process which is easy and suitable forincrease in the area, the thin film transistor 20-1 having thetop-contact structure with suppressed deterioration is obtained withhigh precision without damaging the organic semiconductor pattern 7 a.

By the effect of the metal material component A of the protection film 9slightly diffused in the surface layer of the organic semiconductorpattern 7 a, corrosion caused by the etchant of the organicsemiconductor pattern 7 a is prevented. That is, the metal materialcomponent expresses corrosion prevention action against the etchant.That is, the film quality of the organic semiconductor pattern 7 a ismaintained, and excellent transistor characteristics are obtained in thethin film transistor 20-1 using the organic semiconductor pattern 7 a.Further, since the metal material component A remains slightly in thesurface layer of the organic semiconductor pattern 7 a, an effect thatthe effective channel length of the thin film transistor becomes shorteris also expected.

Moreover, by the wet etching performed at the time of forming the sourceelectrode 13 s and the drain electrode 13 d, the etchant component B inthe etchant is slightly diffused in the surface layer of thesemiconductor pattern 7 a. Therefore, an effect that ohmic contactbetween the organic semiconductor pattern 7 a and the source electrode13 s and the drain electrode 13 d is realized by the etchant component Bis also expected.

2. Second Embodiment

FIGS. 4A and 4B are sectional process drawings expressing acharacteristic part of a method of manufacturing a thin film transistoraccording to a second embodiment. The second embodiment is similar tothe first embodiment except that the organic semiconductor pattern 7 ais over-etched.

First, by wet-etching the electrode material film 13 using the resistpattern 15 as a mask, the source electrode 13 s and the drain electrode13 d are formed. Those processes are similar to those described in thefirst embodiment with reference to FIGS. 1A to 1D and FIGS. 2A to 2C.

In the embodiment, after that, as shown in FIG. 4A, by over-etching theorganic semiconductor pattern 7 a exposed from the source electrode 13 sand the drain electrode 13 d, a process of removing the surface layer ofthe organic semiconductor pattern 7 a is performed. In this case,over-etching of removing the surface layer of the organic semiconductorpattern 7 a by dry etching is performed.

After that, the resist pattern 15 is peeled off and removed. The peelingof the resist pattern 15 may be performed in a manner similar to thefirst embodiment.

By the process, a thin film transistor 20-2 having the top-contactbottom-gate structure shown in FIGS. 4B and 3 is obtained.

Also in the thin film transistor 20-2 obtained in such a manner, an endface of each of the source electrode 13 s and the drain electrode 13 disolated from each other above the organic semiconductor pattern 7 s hasa shape which is isotropically etched by wet etching in a manner similarto the first embodiment. Particularly, the surface layer of the organicsemiconductor pattern 7 a exposed from the source electrode 13 s and thedrain electrode 13 d is over-etched and has a slightly recessed shape.

Also in the second embodiment, the source electrode 13 s and the drainelectrode 13 d are shaped by etching the electrode material film 13using the resist pattern 15 as a mask. Consequently, in a manner similarto the first embodiment, while applying the process which is easy andsuitable for increase in the area, the thin film transistor 20-2 havingthe top-contact structure with suppressed deterioration is obtained withhigh precision without damaging the organic semiconductor pattern 7 a.

Particularly, even in the case where the organic semiconductor pattern 7a is damaged at the time of wet etching performed for forming the sourceelectrode 13 s and the drain electrode 13 d, the surface layer in thispart is removed by over-etching. Consequently, occurrence of parasitictransistor or the like is suppressed, and reliability of the deviceimproves.

3. Third Embodiment

FIGS. 5A to 5D are sectional process drawings expressing acharacteristic part of a method of manufacturing a thin film transistoraccording to a third embodiment. The third embodiment is similar to theforegoing embodiments except that the protection film pattern 9 a isleft on the organic semiconductor pattern 7 a.

First, as shown in FIG. 5A, by dry-etching the organic semiconductorlayer 7 over the protection film pattern 9 a made of a metal material,the organic semiconductor pattern 7 a is formed. Those processes areperformed in a manner similar to those described in the first embodimentwith reference to FIGS. 1A to 1D. As the material of the protection filmpattern 9 a, a material by which a film is formed without damaging theorganic semiconductor layer 7 and which comes into ohmic contact withthe organic semiconductor layer 7 a is selected and used.

In a manner similar to the first embodiment, since the protection filmpattern 9 a made of the metal material is provided in contact with theorganic semiconductor layer 7, the metal material component A of theprotection film pattern 9 is slightly diffused in the surface layer ofthe organic semiconductor layer 7.

The third embodiment is characterized in that, after that, as shown inFIG. 5B, without removing the protection film pattern 9 a, the organicsemiconductor pattern 7 a and the protection film pattern 9 a arecovered with the electrode material film 13. The electrode material film13 is formed in a manner similar to the first embodiment explained withreference to FIG. 2A. The material of the electrode material film 13 maybe selected without necessity of considering damage at the time of filmformation on the organic semiconductor pattern 7 a and ohmic contactwith the organic semiconductor pattern 7 a. The electrode material film13 may be made of the same material as that of the protection filmpattern 9 a or may be made of a different material.

After that, as shown in FIG. 5C, the resist pattern 15 is formed on theelectrode material film 13 in a manner similar to the first embodiment.

Next, using the resist pattern 15 as a mask, the electrode material film13 is etched first. By the etching, the source electrode 13 s and thedrain electrode 13 d are formed, which are isolated from each otherabove the organic semiconductor pattern 7 a and have a shape that an endportion is stacked on the organic semiconductor pattern 7 a in positionswhere they face each other while sandwiching the gate electrode 3.

In the third embodiment, following the etching for the electrodematerial film 13, the protection film pattern 9 a is etched. Theprotection film pattern 9 a made of the metal material is left in partswhere the source electrode 13 s and the drain electrode 13 d are stackedon the organic semiconductor pattern 7 a. By the parts where theprotection film pattern 9 a is left, a part of the source electrode 13 sand a part of the drain electrode 13 d is made thick.

The electrode material film 13 and the protection film pattern 9 a areetched by wet etching. As etchant, an etchant similar to that for theprotection film 9 and the electrode material film 13 is used. By aneffect of the metal material component A of the protection film 9slightly diffused into the surface layer of the organic semiconductorpattern 7 a, corrosion caused by the etchant for the organicsemiconductor pattern 7 a is prevented. By the wet etching, the etchantcomponent B in the etchant is slightly diffused in the surface layer ofthe semiconductor pattern 7 a.

After the source electrode 13 s and the drain electrode 13 d are formedby wet etching, the resist pattern 15 is removed. Removal of the resistpattern 15 is performed in a manner similar to that of the resistpattern 11.

As a result, a thin film transistor 20-3 having the top-contactbottom-gate structure shown in FIGS. 5D and 3 is obtained.

Also in the thin film transistor 20-3 obtained in such a manner, an endface of each of the source electrode 13 s and the drain electrode 13 disolated from each other above the organic semiconductor pattern 7 a hasa shape which is isotropically etched by wet etching. In particular, theparts stacked on the organic semiconductor pattern 7 a in the sourceelectrode 13 s and the drain electrode 13 d in the thin film transistor20-3 are thickened. The parts are thickened by stacking the part made bythe electrode material film 13 on the protection film pattern 9 a whichis in ohmic contact with the organic semiconductor pattern 7 a.

Also in the embodiment, the source electrode 13 s and the drainelectrode 13 d are shaped by etching the electrode material film 13 andthe protection film pattern 9 a using the resist pattern 15 as a mask.Consequently, in a manner similar to the first embodiment, whileapplying the process which is easy and suitable for increase in thearea, the thin film transistor 20-3 having the top-contact structurewith suppressed deterioration is obtained with high precision withoutdamaging the organic semiconductor pattern 7 a.

As long as the protection film pattern 9 a left on the organicsemiconductor pattern 7 a is in ohmic contact with the organicsemiconductor pattern 7 a, the source electrode 13 s and the drainelectrode 13 d part formed by the electrode material film 13 may beselected without considering the ohmic contact. Consequently, as thematerial of the source electrode 13 s and the drain electrode 13 d, acheap material may be used and the cost may be reduced.

Although the source electrode 13 s and the drain electrode 13 d partstacked on the organic semiconductor pattern 7 a is generally formedwith small line width, the part is thickened by the protection filmpattern 9, so that the structure is reinforced.

In a manner similar to the first embodiment, by the metal materialcomponent A of the protection film 9 slightly diffused in the surfacelayer of the organic semiconductor pattern 7 a, corrosion caused by theetchant for the organic semiconductor pattern 7 a is prevented, and aneffect that the thin film transistor 20-3 obtains excellentcharacteristics is also expected. Another effect is also expected thatbecause of slight residual of the metal material component A in thesurface layer of the organic semiconductor pattern 7 a, the effectivechannel length of the thin film transistor becomes shorter.

Further, by the wet etching at the time of forming the source electrode13 s and the drain electrode 13 d, the etchant component B in theetchant is slightly diffused in the surface layer of the semiconductorpattern 7 a. Consequently, in a manner similar to the first embodiment,an effect is expected that ohmic contact between the organicsemiconductor pattern 7 a and the source electrode 13 s and the drainelectrode 13 d is realized by the etchant component B.

In the third embodiment, after the source electrode 13 s and the drainelectrode 13 d are formed in the process of FIG. 5C, as described in thesecond embodiment, the surface layer exposed in the organicsemiconductor pattern 7 s may be over-etched. Therefore, even in thecase where the organic semiconductor pattern 7 a is damaged at the timeof wet etching performed for forming the source electrode 13 s and thedrain electrode 13 d, the surface layer in this part is removed byover-etching. Consequently, occurrence of parasitic transistor or thelike is suppressed, and reliability of the device improves.

4. Fourth Embodiment

FIGS. 6A to 6D and FIGS. 7A to 7C are sectional process drawingsexpressing a characteristic part of a method of manufacturing a thinfilm transistor according to a fourth embodiment. The fourth embodimentis similar to the foregoing embodiments except that a carrier injectionmaterial is used for a protection film and a protection film pattern andis left.

First, as shown in FIG. 6A, the gate electrode 3 is formed in a patternon the insulating substrate 1, the gate insulating film 5 is formed soas to cover the gate electrode 3 and, further, the organic semiconductorlayer 7 is formed on the gate insulating film 5. Those processes aresimilar to those described in the first embodiment with reference toFIG. 1A and are performed by a normal procedure.

As shown in FIG. 6B, a protection film 9′ made of the carrier injectionmaterial is formed on the organic semiconductor layer 7. As the carrierinjection material, for example, when a thin film transistor to beformed is of the p-channel type, an organic material of a hole injectiontype may be used. Examples of the material includepoly(3,4-ethylenedioxythiophene)/poly(4-styrenesulphonate) (PEDOT/PSS),tetrathiofulvalene/tetracyanoquinodimethane) (TTF/TCNQ),tetrafluoro-tetracyanoquinodimethane (F4 TCNQ).

The protection film 9′ may be formed by applying a method properlyselected from the vacuum deposition methods such as resistance heatingevaporation and sputtering and the above-described various methods inaccordance with a material to be used.

Next, as shown in FIG. 6C, the resist pattern 11 is formed in a mannersimilar to the first embodiment on the protection film 9′ in a positionwhere it overlays the gate electrode 3.

As shown in FIG. 6D, using the resist pattern 11 as a mask, theprotection film 9′ and the organic semiconductor layer 7 are etched. Inthis case, the protection film 9′ and the organic semiconductor layer 7are continuously etched by dry etching, thereby forming a protectionfilm pattern 9 a′ made of the carrier injection material. By theprocess, the organic semiconductor pattern 7 a is formed in a pattern soas to cover a part of the gate electrode 3 in the width direction of thegate electrode 3, and the thin film transistor is isolated. Aftercompletion of etching, the resist pattern 11 is removed.

The protection film 9′ may be etched by wet etching. In this case, as anetchant, an orthogonal solvent for the organic semiconductor layer, likealcohol such as ethanol or water is used.

As shown in FIG. 7A, without removing the protection film pattern 9 a′,the organic semiconductor pattern 7 a and the protection film pattern 9a′ are covered with the electrode material film 13. The electrodematerial film 13 may be formed in a manner similar to the firstembodiment described with reference to FIG. 2A. The electrode materialfilm 13 is made of a material which is in ohmic contact with theprotection film pattern 9′. As such a material, from the viewpoint ofohmic contact with the protection film pattern 9′, gold (Au), platinum(Pt), silver (Ag), copper (Cu), aluminum (Al), nickel (Ni), chromium(Cr), molybdenum (Mo), alloys and oxides of those elements, and the likeare preferably used.

After that, as shown in FIG. 7B, the resist pattern 15 is formed on theelectrode material film 13 in a manner similar to the first embodiment.Further, using the resist pattern 15 as a mask, the electrode materialfilm 13 is etched. By the operation, the source electrode 13 s and thedrain electrode 13 d are formed in a shape that an end portion isstacked on the organic semiconductor pattern 7 a in positions where theelectrodes face each other while sandwiching the gate electrode 3.

As the etching for the electrode material film 13, wet etching isemployed in a manner similar to the first embodiment. In the wetetching, by the protection film pattern 9 a′, the organic semiconductorpattern 7 a is not corroded by an etchant. Thus, reliability of the TFTis assured.

After the source electrode 13 s and the drain electrode 13 d are formedby wet etching, the resist pattern 15 is removed in a manner similar tothe first embodiment.

As a result, a thin film transistor 20-4 having the top-contactbottom-gate structure shown in FIGS. 7C and 3 is obtained.

In the thin film transistor 20-4 obtained in such a manner, an end faceof each of the source electrode 13 s and the drain electrode 13 disolated from each other above the organic semiconductor pattern 7 a hasa shape which is isotropically etched by wet etching. In particular, thethin film transistor 20-4 is obtained by stacking the protection filmpattern 9 a′ made of the carrier injection organic material on theorganic semiconductor pattern 7 a. The protection film pattern 9 a′ issandwiched between the organic semiconductor pattern 7 a and the sourceelectrode 13 s and the drain electrode 13 d.

Also in the fourth embodiment, the source electrode 13 s and the drainelectrode 13 d are shaped by etching the electrode material film 13using the resist pattern 15 as a mask. Consequently, in a manner similarto the first embodiment, while applying a process which is easy and alsosuitable to increase the area, the thin film transistor 20-4 having thetop-contact structure with suppressed deterioration is obtained withhigh precision without damaging the organic semiconductor pattern 7 a.

In particular, since the source electrode 13 s and the drain electrode13 d are disposed via the protection film pattern 9 a′ made of thecarrier injection organic material on the organic semiconductor pattern7 a, the organic semiconductor pattern 7 a is protected with theprotection film pattern 9 a′. With the configuration, the film qualityof the organic semiconductor pattern 7 a is maintained excellently, andexcellent transistor characteristics are obtained in the thin filmtransistor 20-4 using the organic semiconductor pattern 7 a.

Further, since formation of the electrode material film 13 does notexert influence on the organic semiconductor pattern 7 a, the option ofthe electrode material film 13 enlarges, and cost may be reduced using acheaper material.

5. Fifth Embodiment

FIGS. 8A to 8D and FIGS. 9A to 9C are sectional process drawingsexpressing a characteristic part of a method of manufacturing a thinfilm transistor according to a fifth embodiment. The fifth embodiment issimilar to the foregoing embodiments except that a protection filmpattern having a stacked structure is left.

First, as shown in FIG. 8A, the gate electrode 3 is foinied in a patternon the insulating substrate 1, the gate insulating film 5 is formed soas to cover the gate electrode 3 and, further, the organic semiconductorlayer 7 is formed on the gate insulating film 5. Those processes aresimilar to those described in the first embodiment with reference toFIG. 1A and are performed by a normal procedure.

As shown in FIG. 8B, a first protection film 9′ made of the carrierinjection material is formed on the organic semiconductor layer 7 and,further, a second protection film 9 made of a metal material is formed.The first protection film 9′ made of the carrier injection material isformed in a manner similar to the protection film 9′ made of the carrierinjection material described in the process of FIG. 6A of the fourthembodiment. The second protection film 9 made of the metal material isformed in a manner similar to the protection film made of the metalmaterial described with reference to FIG. 1B in the first embodiment.For the second protection film 9 made of the metal material, a materialwhich is ohmic contact with a first protection film pattern 9 a-1 madeof the carrier injection material is selectively used.

Next, as shown in FIG. 8C, the resist pattern 11 is formed in a mannersimilar to the first embodiment on the second protection film 9 in aposition where it overlaps the gate electrode 3 and, subsequently, thesecond protection film 9 is etched using the resist pattern 11 as amask. The second protection film 9 made of the metal material is etchedby wet etching in a manner similar to the first embodiment.

Subsequently, as illustrated in FIG. 8D, the first protection film 9′ isetched. By the process, a protection film pattern 9A obtained bystacking a first protection film pattern 9 a-1 made of the carrierinjection material and a second protection film pattern 9 a-2 made of ametal material in order on the organic semiconductor layer 7 is formed.The first protection film 9′ made of the carrier injection material isetched by dry etching in a manner similar to the fourth embodiment.

Subsequent to the etching of the first protection film 9′, the organicsemiconductor layer 7 a is etched, and the organic semiconductor pattern7 a is formed in a state where a part of the gate electrode 3 is coveredin the width direction of the gate electrode 3. The organicsemiconductor layer 7 a is etched by the same process as the dry etchingof the first protection film 9′, thereby isolating a thin filmtransistor to be formed. After completion of the etching, the resistpattern 11 is removed. Etching of the first protection film 9′ made ofthe carrier injection material may be wet etching. In this case, as anetchant, an orthogonal solvent for the organic semiconductor layer, likealcohol such as ethanol or water is used.

Subsequently, as shown in FIG. 9A, the protection film pattern 9A iscovered with the electrode material film 13. The electrode material film13 is formed in a manner similar to the first embodiment described withreference to FIG. 2A.

After that, as shown in FIG. 9B, the resist pattern 15 is formed on theelectrode material film 13 in a manner similar to the first embodiment.Further, using the resist pattern 15 as a mask, the electrode materialfilm 13 is etched. By the operation, the source electrode 13 s and thedrain electrode 13 d are formed in a shape that an end portion isstacked on the organic semiconductor pattern 7 a in positions where theelectrodes face each other while sandwiching the gate electrode 3.

Subsequent to the etching for the electrode material film 13, the secondprotection film pattern 9 a-2 made of a metal material is etched. As aresult, the second protection film pattern 9 a-2 made of a metalmaterial is left in parts in which the source electrode 13 s and thedrain electrode 13 d are stacked on the organic semiconductor pattern 7a. By the left part of the second protection film pattern 9 a-2, a partof the source electrode 13 s and the drain electrode 13 d is thickened.

The electrode material film 13 and the second protection film pattern 9a-2 made of a metal material are etched by wet etching. As an etchant,an etchant similar to that used in the etching of the protection film 9and the electrode material film 13 is used.

After the source electrode 13 s and the drain electrode 13 d are formedby wet etching, the resist pattern 15 is removed. The resist pattern 15is removed in a manner similar to the above-described removal of theresist pattern 11.

As a result, a thin film transistor 20-5 having the top-contactbottom-gate structure shown in FIGS. 9C and 3 is obtained.

In the thin film transistor 20-5 obtained in such a manner, an end faceof each of the source electrode 13 s and the drain electrode 13 disolated from each other above the organic semiconductor pattern 7 a hasa shape which is isotropically etched by wet etching like in the firstembodiment. In particular, in a manner similar to the fourth embodiment,the thin film transistor 20-5 is obtained by stacking the firstprotection film pattern 9 a-1 made of the carrier injection organicmaterial on the organic semiconductor pattern 7 a. In a manner similarto the third embodiment, a part stacked on the organic semiconductorpattern 7 a in the source electrode 13 s and the drain electrode 13 d isthickened by the second protection film pattern 9 a-2 made of the metalmaterial.

Also in the fifth embodiment, the source electrode 13 s and the drainelectrode 13 d are shaped by etching the electrode material film 13using the resist pattern 15 as a mask. Consequently, in a manner similarto the first embodiment, while applying a process which is easy and alsosuitable to increase the area, the thin film transistor 20-4 having thetop-contact structure with suppressed deterioration is obtained withhigh precision without damaging the organic semiconductor pattern 7 a.

In addition, in a manner similar to the fourth embodiment, the filmquality of the organic semiconductor pattern 7 a is maintainedexcellently by being protected by the first protection film pattern 9a-1 made of the carrier injection material, and excellent transistorcharacteristics are obtained in the thin film transistor 20-4 using theorganic semiconductor pattern 7 a. Further, since formation of theelectrode material film 13 and the second protection film 9 made of themetal material does not exert influence on the organic semiconductorpattern 7 a, the option of the electrode material film 13 enlarges, andcost may be reduced using a cheaper material.

In a manner similar to the third embodiment, as long as the secondprotection film pattern 9 a-2 made of a metal material is in ohmiccontact with the first protection film pattern 9 a-1 made of a carrierinjection material, the source electrode 13 s and the drain electrode 13d part formed by the electrode material film 13 may be selected withoutconsidering the ohmic contact. Consequently, as the material of thesource electrode 13 s and the drain electrode 13 d, a cheap material maybe used and the cost may be reduced.

Although the source electrode 13 s and the drain electrode 13 d partstacked on the organic semiconductor pattern 7 a is generally formedwith small line width, the part is thickened by the second protectionfilm pattern 9 a-2, so that the structure is reinforced.

In the foregoing first to fifth embodiments, the configuration offorming the organic semiconductor pattern 7 a by formation of an organicsemiconductor layer and patterning of the formed organic semiconductorlayer has been described. However, the foimation of the semiconductorpattern 7 a is not limited to the procedure but may be the followingmethods. For example, patterning by vapor deposition using a metal mask,patterning using a print shadow mask, patterning by liftoff process,further, patterning to which a printing method such as ink jet printing,reverse offset printing, or microcontact printing is applied, and thelike may be applied.

Further, also to formation of the semiconductor pattern 7 a and theprotection film pattern 9 a′ made of the carrier injection materialdescribed with reference to FIGS. 6A to 6D in the fourth embodiment,patterning by vapor deposition using a metal mask, patterning using aprint shadow mask, patterning by liftoff process, further, patterning towhich a printing method such as ink jet printing, reverse offsetprinting, or microcontact printing is applied, and the like may beapplied.

In the foregoing first to fifth embodiments, the thin film transistor ofthe top contact type using organic semiconductor as a channel is stablyrealized. In application fields requiring high mobility, the contactresistance between the organic semiconductor layer and the source-drainelectrode has to be reduced further. This is because, even whensemiconductor of high mobility is used, if the contact resistance ishigh, mobility of an entire device is limited. One of methods ofreducing contact resistance is a method of increasing carrier injectionefficiency by controlling the work function of the electrode material byelectrode modification or the like. It is however difficult to introducesuch a technique in the organic thin film transistor of the top contacttype. In the following embodiment, the method of increasing carriermobility by reducing the contact resistance between the organicsemiconductor layer and the source and drain electrode will bedescribed.

6. Sixth Embodiment

FIGS. 10A to 10D are sectional process drawings expressing acharacteristic part of a method of manufacturing a thin film transistoraccording to a sixth embodiment. Since the processes of the sixthembodiment are the same as those of the first embodiment up to theprocess of FIG. 2A, the subsequent processes will be described.

After the protection film pattern 9 a is peeled off in the process ofFIG. 10A (FIG. 2A), as shown in FIG. 10B, a surface process is performedwith a surface treatment agent on the surface of the organicsemiconductor pattern 7 a. The surface treatment agent containsmolecules which chemically react with the metal material such as gold(Au) remaining in the surface layer of the organic semiconductor pattern7 a. Concrete examples of the molecule include organosulfur molecules ofthiols, disulfides, and the like, organic selenium/tellurium molecules,nitrile compound, organic silane compound, carboxylic acids, phosphonicacids, phosphoesters, unsaturated hydrocarbons, alcohol aldehyde,halide, diazo compound, and the like. The surface treatment may beperformed in a gas phase or in a solution.

In the embodiment, for example, pentafluorobenzenethiol is used as thesurface treatment agent. In vapor of pentafluorozenzenethiol, reactionbetween gold (Au) A remaining in the surface layer of the organicsemiconductor pattern 7 a and a thiol molecule C is made. By thereaction, the gold molecule A and the thiol molecule C are chemicallycombined, and contact resistance between the source electrode 13 s andthe drain electrode 13 d formed by the same Au later and the organicsemiconductor pattern 7 a is reduced. Although the thiol molecules C aredispersed in this case, they may be formed in a layer state on thesurface of the organic semiconductor pattern 7 a. In any of the cases,it is desirable to eliminate the thiol molecules C in the region betweenthe source electrode 13 s and the drain electrode 13 d to be formedlater simultaneously with Au remaining in the surface layer of theorganic semiconductor pattern 7 a by over-etching similar to that in thesecond embodiment. By the process, occurrence of a parasitic transistoror the like is suppressed and reliability of the device improves.

Subsequently, as shown in FIG. 10C, the electrode material film 13 madeof, for example, Au is formed on the gate insulating film 5 so as tocover the organic semiconductor pattern 7 a. Since the process issimilar to that of FIG. 2B, the details will not be repeated.

Next, as shown in FIG. 10D, a resist pattern (not shown) is formed onthe electrode material film 13 and, using the resist pattern as a mask,the electrode material film 13 is etched. By the etching, the sourceelectrode 13 s and the drain electrode 13 d are formed. After that, theresist pattern is removed.

In the embodiment as described above, prior to formation of the sourceelectrode 13 s and the drain electrode 13 d, the surface of the organicsemiconductor pattern 7 a is subjected to surface treatment withtetrafluorobenzenethiol to make reaction between Au residing in thesurface of the organic semiconductor pattern 7 a andtetrafluorobenzenethiol. As a result, contact resistance between theorganic semiconductor pattern 7 a and each of the source electrode 13 sand the drain electrode 13 d is reduced, and the carrier mobility may beincreased. Therefore, to the fields requiring high mobility, an organicthin film transistor of the top contact type is applied. The othereffects are similar to those of the first embodiment.

FIG. 11 illustrates the relation between gate voltage (V) and draincurrent (A) in the case where the drain voltage is set to −12V, of eachof a thin film transistor (example 1) subjected to the surface treatmentby the embodiment and a thin film transistor (comparative example)obtained without the surface treatment. The parameters are the sameexcept for the presence or absence of the surface treatment. In thediagram, P1 illustrates the example 1, and P2 illustrates thecomparative example. The contact resistance of the comparative exampleis 6.8 kΩ·cm and, in contrast, that of the example 1 is 2.7 kΩ·cm. It isunderstood that the contact resistance is largely reduced as comparedwith that of the comparative example.

7. Seventh Embodiment

FIGS. 12A to 12D are sectional process drawings expressing acharacteristic part of a method of manufacturing a thin film transistoraccording to a seventh embodiment. In the seventh embodiment, an organiccomplex pattern as a carrier injection layer is interposed between theorganic semiconductor pattern 7 a and each of the source electrode 13 sand the drain electrode 13 d. Since the processes of the seventhembodiment are also the same as those of the first embodiment up to theprocess of FIG. 2A, the subsequent processes will be described.

After the protection film pattern 9 a is peeled off by, for example, wetetching in the process of FIG. 2A, as shown in FIG. 12A, a mask 21 madeof metal is formed on the organic semiconductor pattern 7 a byphotolithography or printing. As the mask 21, the protection filmpattern 9 a may not be peeled off but may be patterned by beingpartially etched and used. Next, an organic charge-transfer complex isformed on the gate insulating film 5 so as to cover the organicsemiconductor pattern 7 a and the mask 21, thereby forming an organiccharge-transfer complex film 22.

The organic charge-transfer complex may be a charge-transfer complex ofan organic donor and an organic acceptor such as TTF-TCNQ, or acharge-transfer complex of an organic molecule and an inorganic ioncompound (pentacene-metal oxide). As a method of forming the organiccharge-transfer complex, vacuum deposition of a complex or co-depositionof a donor and an acceptor may be mentioned. Alternatively, any of theabove-described various printing methods may be used.

In this case, the organic charge-transfer complex has a composition of(D: donor) x-(A: acceptor) y. Examples of the donor molecule includepolypyrrole and polypyrrole substitute, polythiophene and polythiophenesubstitute, isothianaphthenes such as polyisothianaphthene, chenylenevinylenes such as polychenylene vinylene, poly(p-phenylenevinylenes)such as poly(p-phenylenevinylene), polyaniline and polyanilinesubstitute, polyacetylenes, polydiacetylenes, polyazulenes, polypyrenes,polycarbazoles, polyselenophenes, polyfurans, poly(p-phenylenes),polyindoles, polypyridazines, polymers and polycyclic condensate such aspolyvinyl carbazole, polyphenylene sulfide, or polyvinylene sulfide,derivatives (triphenodioxazine, triphenodithiazine, hexacene-6,15-quinone, or the like) obtained by substituting oligomers having thesame repeating unit as that of the polymer in the material, acenes suchas naphthacene, pentacene, hexacene, dibenzopentacene,tetrabenzopentacene, pyrene, dizenzopyrene, chrysene, perylene,coronene, terrylene, ovalene, quaterrylene, and circumanthracene, and apart of carbon in the acenes with a functional group such as atoms of N,S, O, or the like, a carbonyl group, or the like, metal phthalocyanines,tetrathiafulvalene and tetrathiafulvalene derivatives,tetrathiapentalene and tetrathiapentalene derivatives, and pigmentalkaline metal ions, alkaline-earth metal ions, transition metal ions,and the like of merocyanine dyes, hemicyanine dyes, and the like.

Examples of the acceptor molecule include a benzene diquinone derivativesuch as DDQ or chloranil and its analog, a cyanoquinodimethanederivative such as DCNQI or TCNQ and its analog, a metal complex such asM(mnt)2 or M(dmit)2 (where M denotes metal atom), naphthalene1,4,5,8-tetracarboxylic acid diimide, N,N′-bis(4-trifuoromethyl benzyl)naphthalene 1,4,5,8-tetracarboxylic acid diimide, N,N′-bis(1H,1H-perfluorooctyl), N,N′-bis(1H, 1H-perfluorooctyl), andN,N′-dioctylnaphthalene 1,4,5,8-tetracarboxylic acid diimide derivative,naphthalene tetracarboxylic acid diimides such as naphthalene 2,3,6,7tetracarboxylic acid diimide, condensed-ring tetracarboxylic aciddiimides such as anthracene tetracarboxylic acid diimides likeanthracene 2,3,6,7-tetracarboxylic acid diimide, fullerenes such as C60,C70, C76, C78, and C84, carbon nanotube such as SWNT and theirderivatives, halogens, metal halide, metal oxide, sulfuric acid, nitricacid, inorganic anion such as perchloric acid.

After formation of the organic charge-transfer complex film 22, bypeeling off the mask 21 as shown in FIG. 12B, the pattern of the organiccharge-transfer complex film 22 is formed. Next, as illustrated in FIG.12C, in a state where the organic semiconductor pattern 7 a and thepattern of the organic charge-transfer complex film 22, the electrodematerial film 13 made of, for example, Au is formed on the gateinsulating film 5. Since the process is similar to that of FIG. 2B, itsdetails will not be described.

Next, as shown in FIG. 12D, a resist pattern (not shown) is formed onthe electrode material film 13 and, by etching the electrode materialfilm 13 using the resist pattern as a mask, the source electrode 13 sand the drain electrode 13 d are formed. After that, the resist patternis removed.

In the embodiment as described above, prior to formation of the sourceelectrode 13 s and the drain electrode 13 d, the pattern of the organiccharge-transfer complex film 22 is formed on the surface of the organicsemiconductor pattern 7 a. Therefore, the organic charge-transfercomplex film 22 functions as the carrier injection layer between theorganic semiconductor pattern 7 a and each of the source electrode 13 sand the drain electrode 13 d. The contact resistance between the organicsemiconductor pattern 7 a and each of the source electrode 13 s and thedrain electrode 13 d is reduced, and the carrier mobility may beincreased. Therefore, also in the embodiment, to the fields requestinghigh mobility, the organic thin film transistor of the top contact typeis applied. The other effects are similar to those of the firstembodiment.

The area ratio between the source electrode 13 s and the drain electrode13 d and the organic charge-transfer complex film 22 on the organicsemiconductor pattern 7 a is not limited. The entire organiccharge-transfer complex film 22 may be hidden below each of theelectrodes or a part of the organic charge-transfer complex film 22 maybe out of each of the electrodes. The organic complex below the sourceelectrode 13 s and that below the drain electrode 13 d are not incontact with each other.

8. Eighth Embodiment

FIGS. 13A to 13C are sectional process drawings expressing acharacteristic part of a method of manufacturing a thin film transistoraccording to an eighth embodiment. In the seventh embodiment, thepattern of the organic charge-transfer complex film 22 is formed byusing the mask 21 made of a metal. In the eighth embodiment, as shown inFIGS. 13A and 13B, at the time of forming the organic charge-transfercomplex film 22, an insulating mask 23 made of, for example, SiO₂ isused. By using the insulating mask 23, the mask 23 is left in thestructure (FIG. 13C), so that the manufacturing process is simplified.Since the rest is the same as the seventh embodiment, the descriptionwill not be repeated.

9. Application Examples

As an example of an electronic device using the thin film transistor ofthe invention described in the foregoing embodiments, a display deviceof an active matrix type using an organic electroluminescence element ELwill be described.

FIG. 14 is a circuit configuration diagram of a display device(electronic device) 30. On the substrate 1 of a display device 30, adisplay region 1 a and a peripheral region 1 b are set. In the displayregion 1 a, a plurality of scanning lines 31 are disposed laterally anda plurality of signal lines 33 are disposed vertically. The displayregion 1 a is constructed as a pixel array in which one pixel “a” isprovided in correspondence with each of intersection points of the scanlines 31 and the signal lines 33. In the peripheral region 1 b, ascanning line drive circuit 35 for driving the scanning lines 31 and asignal line drive circuit 37 for supplying a video signal (that is,input signal) according to brightness information to the signal lines 33are disposed.

A pixel circuit provided at each of the intersecting points of thescanning lines 31 and the signal lines 33 is constructed by, forexample, a thin film transistor Tr1 for switching, a thin filmtransistor Tr2 for driving, a retention capacitor Cs, and an organicelectroluminescence element EL. As the thin film transistors Tr1 andTr2, any of the thin film transistors 20-1 to 20-5 is used.

In the display device 30, by driving of the scanning line drive circuit35, a video signal written from the signal line 33 via the thin filmtransistor Tr1 for switching is held in the retention capacitor Cs.Current according to the amount of signal held is supplied from the thinfilm transistor Tr2 for driving to the organic electroluminescenceelement EL, and the organic electroluminescence element EL emits lightwith brightness according to the current value. The thin film transistorTr2 for driving is connected to a common power supply line (Vcc) 39.

The configuration of the pixel circuit described above is just anexample. As necessary, a capacitive element may be provided in the pixelcircuit or a pixel circuit may be constructed by providing a pluralityof transistors. To the peripheral region 1 b, a necessary drive circuitis added according to change in the pixel circuit.

FIG. 15 expresses a sectional structure of the display device 30 havingthe above-described circuit configuration. The diagram illustrates astructure of one pixel in which the thin film transistors Tr2 and Tr1,the capacitive element Cs, and the organic electroluminescence elementEL are stacked.

The diagram illustrates an example of providing the thin film transistor20-1 having the top-contact bottom-gate structure shown in FIG. 2D inthe first embodiment as the thin film transistors Tr2 and Tr1 providedfor each pixel “a”.

The source electrode 13 s of the thin film transistor Tr1 and the gateelectrode 3 of the thin film transistor Tr2 are connected to each othervia a connection hole 5 a provided for the gate insulating film 5. Thecapacitive element Cs is constructed by making the gate insulating film5 sandwiched between an extension part of the gate electrode 3 in thethin film transistor Tr2 and an extension part of the source electrode13 s. As illustrated also in the circuit diagram of FIG. 14, the gateelectrode 3 of the thin film transistor Tr1 is extended to the scanningline 31, the drain electrode 13 d of the thin film transistor Tr1 isextended to the signal line 33, and the source electrode 13 s of thethin film transistor Tr2 is extended to the power supply line 39.

The thin film transistors Tr1 and Tr2 and the capacitive element Cs arecovered, for example, with an interlayer insulating film 41 via aprotection film. The interlayer insulating film 41 is preferablyconstructed as a planarized film. The interlayer insulating film 41 isprovided with a connection hole 41 a reaching the drain electrode 13 dof the thin film transistor Tr2.

Each of the pixels on the interlayer insulating film 41 is provided withthe organic electroluminescence element EL connected to the thin filmtransistor Tr2 via the connection hole 41 a. The organicelectroluminescence element EL is isolated by an insulating pattern 43provided on the interlayer insulating film 41.

The organic electroluminescence element EL has a pixel electrode 45provided on the interlayer insulating film 41. The pixel electrode 45 isformed as a conductive pattern for each pixel and is connected to thedrain electrode 13 d of the thin film transistor Tr2 via the connectionhole 41 a provided for the interlayer insulating film 41. Such a pixelelectrode 45 is used as, for example, an anode.

The periphery of the pixel electrode 45 is covered with the insulatingpattern 43 for isolating the organic electroluminescence element EL. Theinsulating pattern 43 has an open window 43 a for widely exposing thepixel electrode 45. The open window 43 a serves as a pixel opening ofthe organic electroluminescence element EL.

An organic layer 47 is provided so as to cover the pixel electrode 45exposed from the insulating pattern 43. The organic layer 47 has astacked structure having at least an organic light emission layer and isobtained by stacking, as necessary, a hole injection layer, a holetransport layer, an organic light emission layer, an electron transportlayer, an electron injection layer, and other layers in order from ananode (the pixel electrode 45) side.

A common electrode 49 is provided so as to cover the organic layer 47and sandwich the organic layer 47 between the pixel electrode 45 anditself. The common electrode 49 is an electrode on the side ofextracting light generated by the organic light emission layer in theorganic electroluminescence element EL and is made of a material havinglight transmitting property. In this case, the pixel electrode 45functions as an anode, so that the common electrode 49 is constructed byusing a material which functions as a cathode at least on the side incontact with the organic layer 47. As also shown in the circuit diagramof FIG. 11, the common electrode 49 is disposed at GND.

A pixel part in which the organic layer 47 is sandwiched between thepixel electrode 45 and the common electrode 49 is a part functioning asthe organic electroluminescence element EL.

Although not shown, in a state where the formation face side of eachorganic electroluminescence element EL is covered with an encapsulationresin made of a light transmissive material, and an opposed substratemade of a light transmissive material is adhered via the encapsulationresin, the display device 30 is constructed.

In the display device 30, the pixel circuit is constructed by using afine thin film transistor having excellent characteristics.Consequently, the pixel electrode 45 is stably driven andmicrofabrication of the pixel is achieved, so that the displaycharacteristic improves.

In the foregoing embodiments, as an example of the electronic devicehaving the thin film transistor, the display device of the active matrixusing the organic electroluminescence element EL is illustrated. Theelectronic device of the invention is applicable widely to a displaydevice having a thin film transistor such as a liquid crystal displaydevice and an electrophoretic display.

Further, as an embodiment of the electronic device of the invention, theinvention is widely applicable to an electronic device having thedisplay device. For example, the invention may be applied to an electricpaper, a digital camera, a notebook-sized personal computer, a portableterminal device such as a cellular phone, and an electronic device suchas a video camera. That is, the invention is applicable to an electronicdevice having a display device in all of fields in which a video signalinput to the electronic device or a video signal generated in theelectronic device is displayed as an image or video image.

Further, the electronic device of an embodiment of the invention is notlimited to the display device. The invention is widely applicable to anelectronic device having the thin film transistor to which a conductivepattern (such as a pixel electrode) is connected. For example, theinvention is applicable also to electronic devices such as an ID tag anda sensor. By using a fine thin film transistor having excellentcharacteristics in such an electronic device, a miniaturized device isstable driven.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

1. A display device including a plurality of pixel circuits, each of the plurality of pixel circuits comprising a first thin film transistor, the first thin film transistor comprising: an organic semiconductor pattern provided on insulating layer over a substrate; and a source electrode and a drain electrode, wherein at least one of end portions of each electrodes is formed directly on the organic semiconductor pattern disposed over the substrate in a state where the source electrode and the drain electrode are isolated above the organic semiconductor pattern, and wherein at least one of a metal material and a material component of an acid-series etching solution is contained in the surface layer of the organic semiconductor pattern.
 2. A display device according to claim 1, wherein the source electrode and drain electrode are formed from alloy.
 3. A display device according to claim 1, wherein the source electrode and drain electrode are formed from alloy containing Mo and Al, or alloy containing Al and Ti.
 4. A display device according to claim 1 further comprising a gate electrode formed between the organic semiconductor pattern and the substrate.
 5. A display device according to claim 1, wherein the pixel circuit further comprising a capacitor to hold video signal, and the first transistor samples a video signal to the capacitor from a signal line.
 6. A display device according to claim 5, wherein the pixel circuit further comprising a capacitor to hold a video signal, and a light emitting element which emits light according to the video signal; and the first transistor supplies current to the light emitting element.
 7. A display device including a plurality of pixel circuits, each of the plurality of pixel circuits comprising a first thin film transistor, the first thin film transistor comprising: an organic semiconductor pattern provided on insulating layer over a substrate; and a source electrode and a drain electrode, wherein at least one of end portions of each electrodes is formed directly on the organic semiconductor pattern disposed over the substrate in a state where the source electrode and the drain electrode are isolated above the organic semiconductor pattern, and wherein at least one of a metal material and a material component of an acid-series etching solution is contained in the organic semiconductor pattern.
 8. A display device according to claim 7, wherein a concentration of the metal material and the material component in the organic semiconductor pattern differ between the side of the source/drain electrode and the side of the insulating layer.
 9. A display device according to claim 8, wherein the metal material or the material component has high concentration distribution in the side of the source/drain electrode of the organic semiconductor pattern.
 10. A display device according to claim 7, wherein the source electrode and drain electrode are formed from alloy.
 11. The display device according to claim 7, wherein the source electrode and drain electrode are formed from alloy of Mo and Al, or alloy of Al and Ti.
 12. A display device according to claim 7 further comprising a gate electrode formed between the organic semiconductor pattern and the substrate.
 13. A display device according to claim 7, wherein the pixel circuit further comprising a capacitor to hold video signal, and the first transistor samples a video signal to the capacitor from a signal line.
 14. A display device according to claim 13, wherein the pixel circuit further comprising a capacitor to hold a video signal, and a light emitting element which emits light according to the video signal; and the first transistor supplies current to the light emitting element. 